WRF ARW User's Guide - MMM - UCAR

WPS
2. sixteen_pt : Sixteen-point overlapping parabolic interpolation
The sixteen_pt overlapping parabolic interpolation method requires sixteen valid source
points surrounding the point (x,y), as illustrated in the figure above. The method works by
fitting one parabola to the points ai1, ai2, and ai3, and another parabola to the points ai2,
ai3, and ai4, for row i, 1 ≤i≤4; then, an intermediate interpolated value pi within row i at
the x-coordinate of the point is computed by taking an average of the values of the two
parabolas evaluated at x, with the average being weighted linearly by the distance of x
from ai2 and ai3. Finally, the interpolated value at (x,y) is found by performing the same
operations as for a row of points, but for the column of interpolated values pi to the ycoordinate
of (x,y).
3. average_4pt : Simple four-point average interpolation
The four-point average interpolation method requires at least one valid source data point
from the four source points surrounding the point (x,y). The interpolated value is simply
the average value of all valid values among these four points.
4. wt_average_4pt : Weighted four-point average interpolation
The weighted four-point average interpolation method can handle missing or masked
source data points, and the interpolated value is given as the weighted average of all valid
values, with the weight wij for the source point aij, 1 ≤ i, j ≤ 2,
given by
w = − x− x + y−
y .
2 2
ij max{0,1 ( i ) ( j ) }
Here, xi is the x-coordinate of aij and yj is the y-coordinate of aij.
5. average_16pt : Simple sixteen-point average interpolation
The sixteen-point average interpolation method works in an identical way to the fourpoint
average, but considers the sixteen points surrounding the point (x,y).
WRF-ARW V3: User’s Guide 3-52